I find it fascinating that after so many decades of support for closures, we’re still stuck in a C-style mentality of passing function-pointers that take an explicit context argument rather than a proper closure object. Witness the design of .NET’s Type.FindInterfaces method:
public virtual Type FindInterfaces (TypeFilter filter, Object filterCriteria);
The TypeFilter argument is a delegate. The Object argument is context that the delegate may require! This is pretty much exactly the old-school C-style way of implementing closures:
/* Yes, pretty crude translation, I know */ TypeArray find_interfaces(int (*type_filter)(Type*, void*), void *argument);
Smalltalk (and Lisps) would do it in the natural way, with a block (a closure):
someType selectInterfaces: [:interface | ... ]
Lisp 1.5, complete with support for lexical closures, appeared in 1959. It’s 2007. That’s forty-eight years.